本案例在之前的基础上进行扩展，传递一个自定义的复数类消息。

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作者：杨丝儿
座右铭：始于兴趣，源于热爱，成于投入。
介绍：爱丁堡大学 人工智能专业。技术兴趣点集中在机器人、人工智能可解释性、数学、物理等等。
聊天吹水QQ群：兔叽的魔术工房 (942848525)
个人博客：discover304.top
个人B站账号：杨丝儿今天也在科学修仙（UP主跨站求个三连加关注）

:sparkles:注意

:sparkles:定义消息

我们设计一个传递复数类型，复数类。

在包下新建msg文件夹，并在文件夹内新建Complex.msg文件

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mkdir msg
touch Complex.msg

编辑Complex.msg文件

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int32 real_part
int32 imaginary_part

:sparkles:添加依赖

编辑包内的package.xml文件添加依赖

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<build_depend>message_generation</build_depend>
<exec_depend>message_runtime</exec_depend>

小贴士：package.xml内已经有大量的待选依赖，直接去掉注释就好
2021-12-30 10-19-27 的屏幕截图

:sparkles:添加配置信息

在包内CMakeLists.txt中修改

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find_package(catkin REQUIRED COMPONENTS
  rospy
  std_msgs # 新增行
  message_generation # 新增行
)

catkin_package(
  CATKIN_DEPENDS message_runtime # 新增行
)

将下面面代码去掉注释

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add_message_files(
  FILEs
  Complex.msg # 修改为类型文件名
)

generate_messages(
  DEPENDENCIES
  std_msgs  # Or other packages containing msgs
)

小贴士：CMakeLists.txt也有大量的注释以及说明内容，可以参考。

:sparkles:重编译

在工作区执行下面的命令。

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catkin_make

如果出现红色报错，需要回溯，看看哪里出现了问题。

:sparkles:使用新类型

修改包内topic_publisher.py代码

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#!/usr/bin/env python3

import rospy
# from std_msgs.msg import Int32
from communicate_bot.msg import Complex

class Publisher():
    # count = 0
    count = Complex()

    def Publisher(self):
        # pass
        self.count.real_part = 0
        self.count.imaginary_part = 0

    def publish(self):
        rospy.init_node('topic_publisher')
        # pub = rospy.Publisher('counter', Int32, queue_size=10)
        pub = rospy.Publisher('counter', Complex, queue_size=10)
        rate = rospy.Rate(2)
        while not rospy.is_shutdown():
            pub.publish(self.count)
            # self.count += 1
            self.count.real_part += 1
            self.count.imaginary_part += 1
            # print(self.count)
            print(f"{self.count.real_part}+{self.count.imaginary_part}i")
            rate.sleep()


if __name__ == '__main__':
    publisher = Publisher()
    publisher.publish()

修改包内topic_subscriber.py代码

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#!/usr/bin/env python3

import rospy
# from std_msgs.msg import Int32
from communicate_bot.msg import Complex

class Subscriber():
    def Subscriber():
        pass

    def listen(self):
        rospy.init_node('topic_subscriber')
        # sub = rospy.Subscriber('counter', Int32, lambda msg : print(msg.data))
        sub = rospy.Subscriber('counter', Complex, lambda msg : print(f"{msg.real_part}+{msg.imaginary_part}i"))
        rospy.spin()
      
      
if __name__ == "__main__":
    subscriber = Subscriber()
    subscriber.listen()

小贴士：自定义的类型有的时候会很大，所以我们可以采用锁存话题（latched）的形式。上传一个消息后，会一直保留到下一个新的同类消息上传。

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pub = rospy.Publisher(<消息名>, <消息类型>, latched=True)

:sparkles:运行效果

:sparkles:附加内容

CMakeLists.txt中的说明/教程：

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################################################
## Declare ROS messages, services and actions ##
################################################

## To declare and build messages, services or actions from within this
## package, follow these steps:
## * Let MSG_DEP_SET be the set of packages whose message types you use in
##   your messages/services/actions (e.g. std_msgs, actionlib_msgs, ...).
## * In the file package.xml:
##   * add a build_depend tag for "message_generation"
##   * add a build_depend and a exec_depend tag for each package in MSG_DEP_SET
##   * If MSG_DEP_SET isn't empty the following dependency has been pulled in
##     but can be declared for certainty nonetheless:
##     * add a exec_depend tag for "message_runtime"
## * In this file (CMakeLists.txt):
##   * add "message_generation" and every package in MSG_DEP_SET to
##     find_package(catkin REQUIRED COMPONENTS ...)
##   * add "message_runtime" and every package in MSG_DEP_SET to
##     catkin_package(CATKIN_DEPENDS ...)
##   * uncomment the add_*_files sections below as needed
##     and list every .msg/.srv/.action file to be processed
##   * uncomment the generate_messages entry below
##   * add every package in MSG_DEP_SET to generate_messages(DEPENDENCIES ...)

下一篇会涉及运行阶段的重命名，链接在这里：TODO正在施工中